2.5" Down-pipe or 3" for the d40???

[NT-Boy]

I'm looking at getting a new exhaust in the next few weeks. The thing is I just don't know what size "Down-pipe" to go with, a 2.5" or 3".

I'm looking at getting a 2.5" mandrel bent exhaust, with a 2.5" D.P., But the guy that's gonna do the exhaust thinks I'm best off going with a 3" D.P.... He said the turbo will spool quicker and that it will have a better flow then the 2.5" DP.

Is going with the 3" DP an overkill, will it be to loud, what are the pro's and con's?

I'm not 18 anymore, so I don't want the Nav to stand out like dogs-bulls or sound like a Mac truck driving down the road with 37's...

Cheers...

 

[Cobez]

3" dump and 2.5" to the back with no muffler. Im nearly 30 and still love it mate. Its not that loud really. Dump pipe isnt for noise, its for flow. 3" into 2.5" pipe is perfect. Lots of spool and your Nav will feel unreal to drive. You wont be disappointed mate!

 

[NT-Boy]

Thanx Cobez, are you running a 3" DP on your car? Did you lose any torque?

 

[Cobez]

Sure am, and no loss at all. Turbo spools alot better and gives the throttle alot more response.

 

[NT-Boy]

Thanks Cobez, your a legend....

 

[mike1303]

Can I ask why you went 2.5 after the dump?

 

[Cobez]

Well the main exhaust restriction is in the factory dump, whilst 2.5" for the exhaust is plenty IMO. 3" is overkill as far as im concerned so i stuck with an aftermarket 2.5" with no mufflers and went with the slightly bigger dump.

 

[Tappet]

The bigger the dump pipe the better. Remember with a turbo charged engine the exhaust is everything up to the turbo. After that it just a means of removing the the mostly spent exhaust gas and directing it somewhere else. Think of the turbo as a water wheel or steam turbine , or that matter even a gas turbine like on a helicopter or turbo prop aircraft, the larger the pressure drop across the turbine, the more efficient it will be.

A 3"dump and 2.5 after is a good compromise in terms of function and fit.